Moving to Design

1
Chapter 9

• Moving to Design

2
Objectives

• Discuss the issues related to the management and
  coordination of the design phase of the SDLC
• Develop a system flowchart
• Develop a structure chart using transaction
  analysis and transform analysis

3
Objectives

• Write pseudocode for structured modules
• Develop a package diagram
• Develop a design class diagram
• Explain the major components and levels of design
• Describe the difference between models produced
  by the structured design and object-oriented
  design

4
Components Requiring Systems DesignFigure 9-1
5
Analysis Objectives to Design ObjectivesFigure
9-2
6
Understanding the Elements of Design

• Design is the process of describing, organizing,
  and structuring the components of a system at
  both the architectural level and at a detailed
  level
• Focused on construction
• Like developing blueprints
• Three questions
• What components require systems design?
• What are the inputs to and outputs of the design
  process?
• How is systems design done?

7
Inputs and Outputs Moving from Analysis to Design

• Design
• Converts functional models from analysis into
  models that represent the solution
• Focused on technical issues
• Requires less user involvement than analysis
• Design may use structured or OO approaches
• Database can be relational, OO or hybrid
• User Interface issues

8
SDLC Phases with Design Phase ActivitiesFigure
9-4
Design and Integrate Network Design the
Application Architecture Design the User
Interfaces Design the System Interfaces Design
and Integrate the Database Prototype for Design
Details Design and Integrate System Controls
9
Project Coordination

• Project teams
• Project schedule
• Information
• CASE Tools
• Team Communication

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Information Stored in the CASE Repository Figure
9-6
11
Structured Approach to Designing the Application
Architecture

• Application software programs
• Designed in conjunction with database and user
  interfaces
• Hierarchy of modules
• Documented with system flowcharts
• Design internal program logic
• Top-down approach
• DFDs with automation boundaries
• Structure charts

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Structured Design ModelsFigure 9-7
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Automation System Boundary

• Partitions data flow processes into manual and
  automated systems
• Processes can be inside or outside boundary
• Data flows can be inside and outside of boundary

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DFD with Automation System Boundary Figure 9-8
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System Flowchart

• Representation of various computer programs,
  files, databases, and associated manual processes
• Graphically describes organization of subsystems
• Can show type of system
• Batch
• Real time

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Common System Flow Chart Symbols Figure 9-9
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System Flow Chart for RMO Figure 9-11
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Structure Chart

• Describes functions and subfunctions of each part
  of system
• Shows relationships between modules of a computer
  program
• Simple and direct method
• Each module performs a specific function
• Each layer in a program performs specific
  activities

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Structure Chart Symbols Figure 9-13
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Structure Chart for Entire Payroll
Program Figure 9-14
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Developing a Structure Chart

• Transaction Analysis
• System flow chart and event table inputs
• Upper-level modules developed first
• Identifies each transaction supported by program
• Transform Analysis
• Computer program transforms inputs into outputs
• Structure charts have input, calculate, and
  output subtrees
• Uses DFD fragments for inputs

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Steps to Create a Structure Chart from a DFD
Fragment

• Determine primary information flow
• Find process that represents most fundamental
  change from input to output
• Redraw DFD with inputs to the left and outputs to
  the right
• Generate first draft structure chart

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Steps to Create a Structure Chart from a DFD
Fragment (Continued)

• Add other modules
• Input
• Data storage
• Output
• Add logic from structured English or decision
  tables
• Make final refinements

24
The Create New Order DFD FragmentFigure 9-17
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Exploded View of Create New Order DFD Figure 9-18
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Rearranged Create New Order DFD Figure 9-19
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First Draft of the Structure Chart Figure 9-20
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Quality of Structure Chart

• Module coupling
• Measure of how module is connected to other
  modules in program
• Module cohesion
• Measure of internal strength of module
• Module performs one defined task
• Highly cohesive and loosely coupled modules are
  desirable

29
Module Algorithm Design Pseudocode

• Describes internal logic of software modules
• Variation of structured English that is closer to
  programming code
• Syntax should mirror development language

30
OO Approach to Design of Application Architecture

• OO analysis forms basis for OO design
• Structure must support OO programming
• Programs cooperate to perform tasks
• No one program module is in-charge
• Consists of sets of computing objects
• Encapsulation and information hiding

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OO Analysis Models to Design Models Figure 9-27
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Package diagrams

• Identifies major components of a system
• High-level diagram in UML
• Similar in function to flow chart
• Determines final program partitions
• Dependencies determined

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RMO CSS Package Diagram Figure 9-28
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Design Class Diagrams

• Shows set of classes and their relationships
• Describes design components within the classes
• More complete than analysis versions of same
  diagrams

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Internal Symbols Used to Design a Design
Class Figure 9-31a
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Internal Symbols for Design Class Figure 9-31b
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Design Class Diagram Development

• Choose single class from class diagram
• Elaborate the attributes
• Identify methods
• Elaborate methods with logic

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Short Form of the Order Design Class Figure 9-34
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Finishing up OO Design

• Inheritance, overriding, and polymorphisms
• Integration with user-interface design, database
  design, and network design